The project described in this proposal is designed to define the biochemical, biologic and pharmacologic significance of hematin-derived anticoagulant (HDA). HDA produces prolongation of clotting times in vitro and in vivo. HDA is a derivative or degradation product which is produced when hematin is allowed to stand in solution or when it is infused into rats. HDA will be purified and identified from in vitro and in vivo sources by chromatographic and spectroscopic techniques. This will test the hypothesis that HDA is a single derivative of hematin (heme) which is capable of interacting with coagulation proteins to produce profound functional effects. The mechanism of interaction of HDA with the specific proteins fibrinogen, thrombin and factor VIII:C will be defined by determining binding affinities and effects on enzymatic function with natural and synthetic substrates. The specific techniques of UV-Vis spectroscopy, equilibrium dialysis and antagonism with iron binding compounds will test the hypothesis that iron or a trace metal is involved in the interaction of HDA with clotting proteins. The production and mechanism of HDA in vivo will be defined with isolated hepatic heme metabolic systems and whole animals. This will test the hypothesis that HDA is a metabolic product of heme and that the mechanism is identical to that seen in vitro. Specific techniques involve radioisotope and pharmacologic probes. Finally, the pharmacologic potential of HDA will be determined by pharmacokinetic and efficacy studies utilizing radiolabelled HDA and various routes of administration. Completion of these studies will define the biochemical, physiologic and pharmacologic significance of HDA.